Because of excellent compatibility with human bone, artificial bone made of apatite can be bonded to the human bone directly. Accordingly, the artificial bone made of apatite has recently been appreciated for effectiveness, finding clinical applications in cosmetic surgery, neurosurgery, plastic surgery, oral surgery, etc. However, artificial ceramic bone such as apatite is not necessarily completely identical with human bone in terms of mechanical properties and physiological properties. For instance, a so-called artificial ceramic bone made only of apatite is harder and more brittle than the human bone. While the human bone is repeatedly subjected to metabolism of absorption and regeneration, the artificial bone made of apatite is not substantially dissolved but semi-permanently remains in human body. The remaining artificial bone breaks human bone at an interface with the human bone, making it likely to cause bone fracture.
Research has recently become active on artificial bone decomposable in the human body, which is closer in composition to human bone than the artificial apatite bone, and various proposals have been made. For instance, JP 11-513590 A discloses a cross-linked apatite/collagen porous body having a network structure, in which collagen and, if necessary, other binders are bonded to hydroxyapatite. Because this cross-linked apatite/collagen porous body is decomposable in human body, human bone is formed in the cross-linked apatite/collagen porous body, and the cross-linked apatite/collagen porous body per se is absorbed in a human body. Accordingly, this cross-linked apatite/collagen porous body can be used for the fixation of vertebra, the filling of bone defects, the repair of fractured bone and, the grafting of periodontal defects, etc. However, this cross-linked apatite/collagen porous body is a simple mixture of collagen and apatite, which does not have a living human bone structure, in which the C-axis of the apatite is oriented along collagen fibers. Further, this cross-linked apatite/collagen porous body has insufficient mechanical strength and poor bone neoplasia.